The present invention relates to a coordinate measuring machine and more particularly to a probe for such a coordinate measuring machine. Even more particularly, the present invention relates to a damping mechanism for damping vibrations in such a probe.
Coordinate measuring machines are used to measure the shape of an object to be measured with a high degree of accuracy. A typical application is the measurement of machine-produced workpieces in the course of quality control during production. The shape of the object is measured by moving the probe to defined points of the object by means of the moving frame, and then determining the current position of the probe or of a feeler element connected to said probe. It is particularly known to scan the object using a feeler pin which is fixed to the probe in order to initiate a read-out operation of the spatial coordinates.
The feeler pin is generally mounted such that it can move in or on the probe. In what is called switching probes, the feeler pin opens a contact when it touches the shape of the object to be measured, with this contact causing the coordinates to be read out. In measuring probes, the deflection of the feeler pin from its rest position is also determined, and this allows a particularly high degree of measurement accuracy.
However, mounting the feeler pin such that it can move may lead to the feeler pin itself vibrating when the probe is moved. The natural vibrations cause disturbances when the probe approaches the object and may lead to measurement inaccuracies. For this reason, it is known to damp the feeler pin of the probe, or more generally to damp the moving part or parts within a probe, by means of a damping member which is arranged in the probe, in order to reduce the vibrations, if not completely eliminate them.
DE 197 31 005 A1 discloses an eddy-current brake as a damping member. This is a magnet arrangement with an air gap where a metallic conductive element, such as a copper sheet, is arranged. When the copper sheet moves in the magnetic field, eddy currents are induced in the copper sheet and, these eddy currents lead to a magnetic field being generated. The induced magnetic field interacts with the outer magnetic field and thus creates a damping effect (“braking effect”). In one exemplary embodiment of this document, the probe is constructed from spring parallelograms which are placed one above the other and in each case permit one direction of movement of the feeler pin. Each spring parallelogram is provided with its own eddy-current brake. In another exemplary embodiment, a single eddy-current brake is provided which damps the feeler pin in the z-direction and in the x-direction. In this exemplary embodiment, a second separate eddy-current brake would be required for damping in the y-direction if necessary.
The principle of the eddy-current brake for damping vibrations in a probe is also known from DE 44 24 225 A1, with the probe again being constructed from spring parallelograms which are placed one above the other and each having their own eddy-current brake.
DE 101 00 350 A1 also discloses a probe comprising spring parallelograms which are placed one above the other, in which a friction brake whose friction force can be adjusted is used as the damping member. U.S. Pat. No. 6,370,788 discloses using a rubber cylinder or, alternatively, glass dust as the damping element. Furthermore, DE 101 47 614 A1 discloses using a viscous damper, that is to say a viscous medium, as the damping element in a coordinate measuring machine.